Dynamic random access memory (DRAM) is a representative example of a semiconductor memory device. In DRAM, information is stored as electric charges on cell capacitors, and therefore the information will eventually be lost if the electric charges are not periodically refreshed. To achieve this, a control device that controls the DRAM device periodically issues a refresh command that tells the DRAM device to perform a refresh operation (see Patent Document 1). The control device issues the refresh command at a frequency that ensures all of the word lines are refreshed once per refresh cycle (which lasts 64 msec, for example).